1. Field of the Invention
The present invention relates to an antenna array and, more particularly, to a dual polarization antenna array having radiating slots and notch dipole elements sharing a common antenna aperture.
2. Description of Related Art
Radar and communication systems commonly use dual polarized antennas which are capable of achieving significant performance advantages over single polarization antenna arrangements. Current trends in radar and communication antenna designs emphasize the reduction of cost and volume of the dual polarization antenna, while achieving high performance. The dual polarization antenna is particularly useful with energy waves such as those employed in the radio frequency spectrum having two orthogonal components which are orthogonally polarized with respect to each other. The first orthogonal component is conventionally known as the vertical or principle polarization component, while the second component is generally known as the horizontal or cross polarization component. The orthogonal polarization of the energy waves allows for the possibility of broadcasting two different signals at the same operating frequency. In doing so, one signal is derived from the principle polarization component and the second signal is derived from the cross polarization component.
The more basic conventional antenna systems are capable of employing the orthogonally polarized signal components to double the information sent at the same frequency by using two separate antennas. One type of conventional dual polarization antenna utilizes a reflector antenna with dual polarization feed elements. This reflector antenna consumes a large volume and is therefore bulky by today's standards. In addition, the conventional reflector arrangement can exhibit a relatively poor efficiency as compared to other types of antennas and often experiences poor isolation between the two polarizations. The conventional dual polarization reflector antenna is also limited in its ability to offer low sidelobe radiation pattern performance.
Another type of dual polarization antenna includes an array of dual polarized patches typically made up of conductive patches fabricated on a dielectric substrate. The dual polarized patch antenna can be manufactured at a low cost and provides for a low profile antenna configuration. However, the bandwidth of each element of the dual polarized patch antenna is typically quite narrow and therefore it is very difficult to achieve a high antenna performance with the patch antenna. Also, the efficiency of the dual polarized patch array antenna can be quite low due to the presence of undesirable dielectric losses.
Another antenna includes a dual polarization rectangular waveguide array 10, as shown in FIG. 1, which consists of a stack up of rectangular waveguide fed offset longitudinal slot arrays 12 and waveguide fed tilted edge slot arrays 14. The offset slots 16 on the longitudinal slot arrays 12 excites both the desirable TEM mode and the undesirable TM.sub.01 odd mode in the parallel plate region formed by the edge slot arrays 14 (see FIG. 1). This undesirable TM.sub.01 odd mode exhibits poor performance. The excited TM.sub.01 odd mode also causes high sidelobes and RF loss. A further limitation in performance of this type of antenna results from the coupling between arrays 12 and 14 caused by the tilted edge slots 18 of the edge slot arrays 14 containing a cross polarization component.
A further approach includes arched notch dipole card arrays 20, as shown in FIG. 2, erected over a rectangular waveguide fed offset longitudinal slot arrays 22. The arched notch dipole card arrays 20 have arches 24 provided to improve the performance of the principal-polarization slot arrays 22 and minimize interactions between the two arrays 20 and 22. However, this type of antenna is difficult to design due to the lack: of a convenient method to account for the presence of the arched dipole arrays 20 in the design of the slot arrays 22. Also, the requirement to maximize the spacing between the face of the slot arrays 22 and the arch arrays 20 to reduce interaction conflicts with the desire to place the notch radiators 26 one-quarter wavelength above the slot array surface for optimal image current formation. Moreover, this limitation becomes especially severe at higher frequencies of operation.
It is therefore desirable to provide for a compact low cost dual polarization antenna array which achieves high performance. More particularly, it is desirable to provide for a dual polarization antenna array which shares a common aperture of radiating slots and notch dipole elements at a low cost and yet exhibits high antenna performance.